1. Field of the Invention
The present invention relates to a toner and a two-component developer to be used in an electrophotographic system, an electrostatic recording system, an electrostatic printing system, or a toner jet system.
2. Description of the Related Art
In recent years, requirements for an increase in printing speed and correspondence to energy savings have been additionally growing in association with the widespread use of a full-color copying machine of an electrophotographic system. A technology for melting a toner in an additionally quick manner in a fixing step has been studied for corresponding to high-speed printing. In addition, a technology by which the toner is fixed at an additionally low fixation temperature in order that a power consumption in the fixing step may be reduced has been studied as measures to correspond to the energy savings.
The following method is available for corresponding to the high-speed printing and improving the low-temperature fixability of the toner. The glass transition point and softening point of the binder resin of the toner are reduced, and a binder resin having sharp-melt property is used. In recent years, a polyester resin has been used as a sharp-melt resin suitable for the high-speed printing. On the other hand, the hot offset resistance of a toner that achieves low-temperature fixability is apt to reduce. Accordingly, a toner that can achieve compatibility between its low-temperature fixability and hot offset resistance has been required.
A toner containing polyester resins having different softening points has been studied in order that compatibility between low-temperature fixability and hot offset resistance may be achieved. For example, Japanese Patent Application Laid-Open No. 2003-280243 proposes such a toner that a value for a loss tangent in the range of a loss modulus G″ of from 1×104 Pa or more to 1×106 Pa or less and the range of a loss tangent at a loss modulus G″ of 1×103 Pa are specified. According to Japanese Patent Application Laid-Open No. 2003-280243, a toner that contains a polyester resin containing novolac as a constituent unit, and hence easily achieves characteristic viscoelasticity and has high-speed fixability is obtained.
In addition, Japanese Patent Application Laid-Open No. 2008-122931 proposes a resin for a toner formed of a polyester resin formed of: a linear polyester that has an acid value of from 50 mgKOH/g or more to 200 mgKOH/g or less, and whose glass transition point and flow softening point satisfy a specific relationship; and a nonlinear polyester.
In addition, Japanese Patent Application Laid-Open No. 2013-105074 proposes a toner binder that contains two polyester resins different from each other in softening point and weight-average molecular weight, and whose ratio between loss tangents at specific temperatures falls within a specific range. Japanese Patent Application Laid-Open No. 2013-105074 describes that when an alkane dicarboxylic acid and/or alkene dicarboxylic acid having 4 or more to 8 or less carbon atoms are each/is incorporated at a content of from 0.1 mol % or more to 10 mol % or less into the polycarboxylic acid component of a polyester resin, the storage stability of a toner and the transparency of the binder upon its use in the toner are good. In addition, the literature describes that when a polyoxyalkylene ether of a novolac resin is incorporated at a content of from 0.02 mol % or more to 10 mol % or less into the polyol component of a polyester resin, the storage stability of the toner is good.
The toner described in Japanese Patent Application Laid-Open No. 2003-280243, and a toner using the resin for a toner described in Japanese Patent Application Laid-Open No. 2008-122931 or the toner binder described in Japanese Patent Application Laid-Open No. 2013-105074 each have some levels of low-temperature fixability and hot offset resistance by virtue of which the toner is applicable to high-speed printing. However, when any such toner is applied to high-speed printing required in recent years in which images are printed on about 100 sheets of paper per minute, its fixability cannot be said to be sufficient. In addition, after long-term printing, a density fluctuation may enlarge or fogging may occur in a white portion.
In addition, Japanese Patent Application Laid-Open No. 2013-33176 proposes a positively chargeable toner containing a polyester resin obtained by condensing a carboxylic acid component, which is selected from the group consisting of an adipic acid compound and a succinic acid compound substituted with an alkyl group or an alkenyl group, in the presence of a titanium catalyst. The toner described in Japanese Patent Application Laid-Open No. 2013-33176 has a high initial charge quantity, and is suppressed in initial fogging and development ghost. However, Japanese Patent Application Laid-Open No. 2013-33176 describes that when the resin is applied to a negatively chargeable toner, an improving effect on the initial charge quantity and an alleviating effect on the initial fogging are not obtained. In addition, when the toner is applied to high-speed printing, its low-temperature fixability is insufficient, or a density fluctuation or fogging after long-term printing increases in some cases.